Vertical semiconductor devices often have electrical connections on different sides of the device. The semiconductor substrate on which a vertical semiconductor device is fabricated can be thinned at its backside so that structures such as emitters, metal contacts or other devices can be formed at the thinned backside of the substrate. For example, an epitaxial layer is typically grown on a highly doped semiconductor substrate and various processes are carried out at the frontside to form an active device region which includes e.g. transistors. The backside of the substrate is then thinned and metal is deposited on the thinned backside to form an electrode. However, the silicon material which remains between the active device region at the frontside and the backside metallization adds resistance to the device. In another conventional approach, a dummy substrate is provided on which an epitaxial layer is grown. The active device region is formed in the epitaxial layer and the dummy substrate is thinned. Structures are then formed on the thinned backside. However, inhomogeneities associated with the substrate thinning process influence key device parameters such as breakdown voltage, forward voltage and on-resistance. Yield-critical vertical devices subjected to such backside processing are particularly sensitive to thickness variations in the active area which result due to variations associated with the thinning process.
In other approaches, the electrode structure is formed within the semiconductor substrate instead of thinning the substrate and depositing the electrode on the thinned backside. Conventional buried electrodes are formed within the semiconductor substrate by doping the substrate in a particular region. An epitaxial layer is grown on the substrate and an active device region is formed in the epitaxial layer. A sinker or trench contact is then formed in the substrate so that the buried layer can be electrically contacted. However, the sinker/trench contact and the buried layer structures both add resistance to the device.